The present invention relates to an optical power limiting material (optical limiting material) which responds to strong light rapidly, more specifically, a novel material which is suitable as a light shutter or a light fuse for protecting naked eyes, sensors, etc. from a strong laser beam or, in the case where an excessively strong laser beam is input into an optical device, for preventing optical device components from being optically damaged by blocking the laser beam.
Materials having an effect of transmitting light well when incident light has low intensity, while regulating transmitted light intensity lower than a certain value when incident light has high intensity, i.e., materials having an optical power limiting effect are known in the art. The optical power limiting materials can be generally divided into two types; one having a reversible response characteristic and the other having a irreversible response characteristic.
The optical power limiting material having the reversible characteristic can be used repeatedly since transmitted light intensity of the material can be returned to the original value even after incident light intensity is increased and then decreased to the original value. On the other hand, the material having the irreversible response characteristic cannot be used repeatedly but only for a single operation since the material has the properties of retaining the same transmitted light intensity even when incident light intensity is increased and then decreased to the original value. Recently, the optical power limiting material having reversible response characteristic has been actively studied, since such optical power limiting material has a greater industrial applicability and usability as compared with the material having irreversible response characteristic.
Rapid response, i.e., properties of responding immediately to strong light input, are required for the protection of naked eyes, sensors, optical device components, etc. from the strong light input. In the case where weak light is irradiated continuously for a long time, it is required that transmitted light intensity remains unchanged. These two are the basic requirements for the optical power limiting material.
Organic materials such as porphyrin derivatives, fullerene, etc. have heretofore been found as possible choices for the materials exhibiting a relatively good optical power limiting effect rapidly.
However, properties of these organic materials are not satisfactory for practical use. For example, since the organic materials do not have satisfactorily high heat resistance, the molecular structure thereof may change irreversibly due to a temperature rise occurring in the case of absorbing extremely strong light or the characteristic thereof may change irreversibly due to thermal decomposition, thereby to lose the optical power limiting effect. Further, the organic materials have such problems that the production thereof is relatively complicated and they can be produced by only a small scale.
In turn, a photochromic material, which reversibly changes in color in response to light, has been investigated as a representative material having a light response function. However, the photochromic material does not satisfy the requirements of the optical power limiting material since the photochromic material is slow in response speed and the light transmitting properties thereof are changed gradually due to responding to week light. Thus, there is a demand for a novel high-performance optical power limiting material.
The problems detected with the conventional materials exhibiting relatively satisfactory optical power limiting properties reversibly are that the insufficient heat resistance with respect to irradiation with a strong laser beam and the complicated and expensive production process. Accordingly, there is a demand for a high-performance optical power limiting material which has a high stability, and can be produced simply and economically (see, First International Workshop on Optical Power Limiting, Cannes (France), 1998).
In view of the present situation of the optical power limiting materials as explained above, a main object of the present invention is to provide a novel high-performance optical power limiting material which is unsusceptible to damages otherwise caused by heat occurring when a strong laser beam is irradiated thereon, has reversible characteristic, exhibits a stable optical power limiting effect and can be produced simply and economically.
The inventors have carried out extensive researches and found that an optical power limiting material comprising a transparent substrate and a specific metal oxide can achieve the above objects, thereby to accomplish the present invention.
The present invention provides the following optical power limiting material and uses thereof.
1. An optical power limiting material comprising a transparent substrate and an oxide of at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ru, In, Sn, Sb, Ta, W, Re, Os, Ir and Bi (except for VO2).
2. The optical power limiting material according to item 1, wherein the transparent substrate is at least one selected from the group consisting of glass, SiO2, Al2O3, ZnO, ZrO2l ZnSe and quartz.
3. The optical power limiting material according to item 2, wherein the transparent substrate is at least one selected from the group consisting of SiO2, Al2O3 and ZrO2.
4. The optical power limiting material according to item 1, wherein the transparent substrate is porous substance.
5. The optical power limiting material according to item 1, wherein the transparent substrate is at least one selected from the group consisting of an acrylic resin, a polycarbonate resin, a polystyrene resin and a polyvinyl resin.
6. The optical power limiting material according to item 1, wherein the metal oxide is at least one selected from the group consisting of TiO, Ti2O3, TiO2, VO, V2O3, V2O5, CrO, Cr2O3, CrO2, Cr2O5, CrO3, CrO5, MnO, Mn3O4, Mn2O3, MnO2, MnO3, Mn2O7, FeO, Fe3O4, Fe2O3, CoO, Co2O3, Co3O4, CoO2, NiO, Ni3O4, Ni2O3, NiO2, Cu2O, CuO, ZnO, NbO, Nb2O3, NbO2, Nb2O5, MoO, Mo2O3, MoO2, Mo2O5, MoO3, RuO, Ru2O3, RuO2, RuO4, In2O, In2O3, SnO, SnO2, Sb2O3, Sb2O4, Sb2O5, TaO2, Ta2O3, Ta2O5, WO2, W2O5, WO3, Re2O, ReO, Re2O3, ReO2, Re2O5, ReO3, Re2O7, OsO, Os2O3, OsO2, OsO3, OsO4, Ir2O3, IrO2, BiO, Bi2O3 and Bi2O5.
7. The optical power limiting material according to item 1, wherein the metal oxide is at least one selected from the group of composite oxides consisting of XCr2O4 (X=Mg, Zn, Cu, Mn, Fe, Co, Ni), Na2SnO3, Pb2SnO4, Bi2Sn2O7, Na3VO4, MVO4 (M=Nd, Sm, Eu, Y, Fe, Cr), VOMo4, MV2O4 (M=Mg, Mn, Co, Zn, Cu), VM2O4 (M=Mg, Co, Zn), VMn2O4, V2MoO8, AxV2O5 (O less than x less than 1, A=Li, K, Na, Cu, Ag, Ca, Cd, Pb), ZrV2O7, MVO3, (M=K, Fe, Ti, Cr, Ni, Mg, Ca, La, Y, Sc), H4(PMo11VO40), H5(PMo10V2O40), H6(PMo9V3O40), H4(PW11VO40), H6(PW6V3O41), Bi2O3.xMoO3 (x=4, 3, 2, 1, {fraction (1/2, 1/3, 1/10)}), Bi2O3.xWO3 (x=2 to 3, 1, xc2xd to ⅕, xc2xd), xBi2O3.Sb2O5 (x=1, 3), Bi9PMo12O52, Fe2(MoO4)3, (MoO3)1.0(Cr2O3)0.75, AxWO3 (0 less than x less than 1, A=H, Li, K, Na, Rb, Ca, Cu, Ag, In, Tl, Sn, Pb, rare earth element), LiTi2O4, MnCo2O4, NiCo2O4 and NiMnCo4O8.
8. The optical power limiting material according to item 1, wherein the metal oxide forms a thin film on a surface of the transparent substrate in the form of particles having a mean particle diameter of not more than 1 xcexcm.
9. The optical power limiting material according to item 1, wherein the metal oxide forms a thin film on a surface of the transparent substrate in the form of particles having a mean particle diameter of not more than 1 xcexcm, and a ratio of a number of metal atoms in the metal oxide to a number of non-oxygen atoms in the oxide comprised in the transparent substrate or a number of monomer units composing a polymer ranges from 1:1 to 1:100.
10. The optical power limiting material according to item 1, wherein the metal oxide is dispersed in the transparent substrate in the form of particles having a mean particle diameter of not more than 1 xcexcm.
11. The optical power limiting material according to item 1, wherein the metal oxide is dispersed in the transparent substrate in the form of particles having a mean particle diameter of not more than 1 xcexcm, and a ratio of a number of metal atoms in the metal oxide to a number of non-oxygen atoms in the oxide comprised in the transparent substrate or a number of monomer units composing a polymer ranges from 1:1 to 1:100.
12. The optical power limiting material according to claim 1, which further comprises a transparent additive component.
13. The optical power limiting material according to claim 12, wherein the transparent additive component is at least one selected from the group consisting of SiO2, Al2O3, ZrO2, ZrO, ZnSe, an acrylic resin, a polycarbonate resin, a polystyrene resin and a polyvinyl resin.
14. The optical power limiting material according to claim 12, wherein the transparent additive component is at least one selected from the group consisting of SiO2, Al2O3, ZrO2, an acrylic resin, a polycarbonate resin, a polystyrene resin and a polyvinyl resin.
15. A light shutter comprising the optical power limiting material according to item 1.
16. A light shutter characterized in that the optical power limiting material according to item 1 is located in the vicinity of a focal point of a condenser lens for condensing incident light.
17. A light fuse comprising the optical power limiting material according to item 1.
18. A light fuse characterized in that the optical power limiting material according to item 1 is located in the vicinity of a focal point of a condenser lens for condensing incident light.